The Kuiper Belt is a region in outer space that extends far beyond the planets in our solar system, but still orbits the Sun.
Since there is very little light out there, it was difficult for scientists to find any evidence that such a thing existed, until one day, when a slow-moving object was recorded moving as if it were orbiting the Sun.
The Kuiper Belt is much like the asteroid belt, but vastly much larger.
Despite being incredibly hard to monitor, scientists have always believed in the Kuiper Belt because it is responsible for loose bodies in space that often come near Earth and other planets, like comets.
With the limited light out there, and the fact that some of those asteroids are thought to be blacker than asphalt, it's hard for scientists to use the Sunlight to their advantage, but maybe NASA's New Horizon's spacecraft will get out there soon without getting smashed to bits.